Modified GIC Estimation Using 3‐D Earth Conductivity

Abstract

Geomagnetically induced currents (GICs) are quasi‐direct current (DC) electric currents that flow in technological conductors during geomagnetic storms. Extreme GICs are hazardous to man‐made infrastructure. GICs enter and exit the technological systems, such as the electric power grid, at grounding points, and their magnitudes depend on the currents that flow underground. They are, therefore, a function of the Earth's electrical conductivity, represented at ground level as Earth impedances, as well as the resistance parameters of the power network. Traditional GIC estimation practices are based on Earth impedances obtained from laterally homogeneous or piecewise layered‐Earth models. We refer to these methods, collectively, as the 1‐D approximation. However, GIC hazard mitigation can be improved with more accurate GIC modeling that takes the spatially heterogeneous Earth's conductivity into account. Here, we propose a modified approximation for GIC estimation that is very similar to the 1‐D approximation but is instead derived from empirical 3‐D Earth impedances. Our formulation sets up the computation of static, frequency‐dependent power line telluric response functions, which, once computed, may be considered part of the power grid system model. These response functions may then be used for historical scenario analysis of GIC hazards and for simplified real‐time, albeit approximate, GIC estimation in a power grid. This modest modification to the simpler local field formulation approach avoids real‐time integration of geoelectric fields along power lines while taking the realistic 3‐D Earth into account in a rigorous manner. Once implemented, the method provides a power grid operator with the benefits of convenience and computational speed for a first look real‐time operational GIC hazard assessment. We estimate that the proposed modified 3‐D GIC modeling approach produces GIC values that are well within 50% of those obtained with the full‐scale power line integration of spatially variable geoelectric fields, for storms comparable in scale to the 2003 Halloween storm, all geological structures, and power lines located in the contiguous United States and other low‐ to middle‐latitude regions.

Modeling the Geomagnetic Response to the September 2017 Space Weather Event Over Fennoscandia Using the Space Weather Modeling Framework: Studying the Impacts of Spatial Resolution

“…If we can accurately model the temporal and spatial characteristics of the surface magnetic field, then useful modeling of GICs should be a straightforward task. This is dependent on knowing the physical properties of the system in question, and possessing a realistic knowledge of the local ground conductivity (Boteler, 2003; Bedrosian & Love, 2015; Pulkkinen et al., 2017; Kelbert & Lucas, 2020). At Mäntsälä, the conductivity is provided by Viljanen, Pulkkinen, et al.…”

“…If we can accurately model the temporal and spatial characteristics of the surface magnetic field, then useful modeling of GICs should be a straightforward task. This is dependent on knowing the physical properties of the system in question, and possessing a realistic knowledge of the local ground conductivity (Boteler, 2003;Bedrosian & Love, 2015;Pulkkinen et al, 2017;Kelbert & Lucas, 2020). At Mäntsälä, the conductivity is provided by Viljanen, Pulkkinen, et al (2006); Viljanen, Tanskanen, et al (2006), and as shown by Equation 1, there is an exact relationship between the geoelectric field and the and GIC (Pulkkinen, Pirjola et al, 2001;Pulkkinen, Viljanen et al 2001) when the geoelectric field is uniform.…”

Evaluating the relationship between strong geomagnetic storms and electric grid failures in Poland using the geoelectric field as a GIC proxy

“…This Earth-layered model for the European regions has already been used in a number of studies (e.g., Viljanen et al, 2013Viljanen et al, , 2014. Differences concerning various methods were emphasized by (e.g., Viljanen et al, 2012;Kelbert & Lucas, 2020).…”

Comparing three approaches to the inducing source setting for the ground electromagnetic field modeling due to space weather events

“…As for the source, approximating it by plane waves still prevails in the GIC-related studies (e.g., Campanya et al, 2019;Kelbert & Lucas, 2020;Kelbert et al, 2017;Lucas et al, 2018;Sokolova et al, 2019;Wang et al, 2020). This approximation seems reasonable in low and middle latitudes, where the main source of anomalous geomagnetic disturbances is a large-scale magnetospheric ring current.…”